A number of techniques are available to transmit signals from a rotatable machine shaft to a stationary receiver located adjacent to the shaft. These techniques include radio frequency telemetry, induction power and signal telemetry, the use of slip rings, and optical telemetry using photovoltaic power and infrared signal telemetry. Each of these techniques requires that a mechanical attachment in the form of a collar must be made between the telemetry components and the rotating shaft.
Various methods have been used to attach the telemetry system to a high speed shaft which include the use of machined one half cylindrical structures which are then bolted to a high speed shaft. This technique is largely unsuccessful due to the relatively high mass of the structure which creates significant bolt stress at speed. Potential bolt failure and catastrophic clamp failure can result from machine overspeed or unknown fatigue characteristics. An infinite variety of machine shaft diameters requires that each structure must be custom machined to fit a particular shaft. This is a costly process.
Other attempts to attach systems to the shaft use an intermediate assembly which replaces the machine coupling with the telemetry coupling device. Typically these devices are not suitable for transferring the high torque loads associated with industrial machinery.
Additional problems are unique to optical telemetry systems. These systems require the use of windows to allow power and data transmission. Typically these windows are made by using glass or clear plastic which often fail in service due to poor strength. In other designs the shaft is modified to provide cavities for the microelectronic components and optical devices which are then epoxied into place. This results in stress concentrations and possible shaft failure.
In every case the telemetry system is difficult to install, expensive to fabricate, mechanically unreliable and often results in reduced strength and reliability of the rotor system.